It has been traditional in assessment of nuclear power plant safety that both deterministic safety analyses and probabilistic safety analyses treat the potential effects of various hazards individually. That is, the safety implications of internal events (e.g., randomly occurring transients and LOCAs), internal hazards (e.g., internal fire and flood), and external hazards (e.g., earthquakes, tornados) are treated as independent occurrences. With the occurrence of the Great Tohoku earthquake and the effects observed at nuclear plants in Japan, it was realized that this approach failed to provide a realistic representation of risk, and now there is a significant interest in correlated hazards.
As a result, EPRI embarked on the development of an improved methodology focusing on seismically-induced internal fires and internal floods. All the technical work on the methodology has been completed and draft technical guidance developed. This guidance has been provided to some plants that are interested in piloting the methodology. As of the date of paper submittal, two pilots are underway and three more are under consideration. Upon completion of the pilots, the methodology will be updated to incorporate the lessons-learned and published.
